NITROGEN OF THE PROTEINS. 77 



belongs); (4) monamino-acid nitrogen; and (5) the nitrogen in variable 

 amounts which appears as humus-like melanoidins, which seem to be 

 of only secondary formation as products of elaboration. 



The quantitative division of the total nitrogen between the above 

 five groups is different in the various protein substances, and more- 

 over cannot be given with certainty, because of the above-mentioned 

 melanoidin formation and the errors in the methods used. 1 The follow- 

 ing gives at least an approximate idea of this division. 2 The loosely 

 combined so-called amide nitrogen seems to. be entirely absent in the 

 protamines. In the gelatins we find 1-2 per cent, and 5-10 per cent 

 in other animal protein substances, 3 in the plant gluten-proteids, 13-20 

 per cent of the total nitrogen is amide nitrogen. The guanidine nitrogen 

 may amount in the protamines to 22-44 per cent of the total nitrogen, 

 in the histones to 12-13 per cent, in the gelatins about 8 per cent, 

 and in the other protein bodies about 2-5 per cent. As basic nitrogen 

 precipitable by phosphotungstic acid (including the guanidine residue) 

 we find 35-88 per cent in the protamines, 35-42.5 per cent in the histones, 

 15-30 per cent in the other animal protein substances, 5-14 per cent 

 in zein and the gluten proteid, and up to 37 per cent in the plant globulins. 

 The chief quantity of the nitrogen, 55-76 per cent, occurs, with the excep- 

 tion of the protamines, as the monamino-acid groups. The results 

 for the melanoidin nitrogen vary so considerably that they will not be 

 mentioned. OSBORNE, LEAVENWORTH and BRAUTLECHT 4 have recently 

 published the results of their investigations on the different forms of 

 binding of the nitrogen in the plant-proteins. 



From the above results it follows that the nitrogen of most protein 

 bodies exists in such combination that the chief quantity appears in the 

 cleavage products as amino-compounds on hydrolytic cleavage by acids. 

 By the action of nitrous acid upon proteins only a very small part, 1-2 

 per cent, of the nitrogen is evolved, 5 which seems to indicate that XH 2 

 groups exist only to a slight extent in protein substances. This assump- 



1 See the work of Hausmann, Zeitschr. f. physiol. Chem., 27 and 29; Henderson, 

 ibid., 27, Kossel and Kutscher, ibid., 30; Kutscher, ibid., 31, 38; Hart, ibid., 33; 

 Giimbel, Hofmeister's Beitrage, 5; Rothera, ibid. 



2 See the works given in footnote 1 and Blum, Zeitschr. f. physiol. Chem., 30; 

 Kossel, Ber. d. d. chem. Gesellsch., 34, 3214; Hofmeister, Ergebnisse der Physiol., 

 Jahrjr. I, Abt. 1, 759, which also contains the literature; Osborne and Harris, Journ. 

 Amer. Chem. Soc., 2t5; and Giimbel, I.e. 



3 Skraup and v. Hardt-Stremayr, Monatsh. f. Chem., 29, found lower results 

 than other investigators and they found also that about two-thirds of the amide 

 nitrogen was readily split off and one-third slowly. 



4 Amer. Journ. of Physiol., 23. 



5 See C. Paal, Ber. d. d. chem. Gesellsch., 29; H. Schiff, ibid., 1354; O. Loew, 

 Chemiker Zeitung, 1896; and O. Nasse, Pfliiger's Arch., 6. 



